Contain c, h, o, and n, central carbon, hydrogen group, acid group (cooh), amino group (nh2) and varying side chain. Non-essenial amino acids: alanine, asparagine, asparic acid, glutamic acid, serine. Condiionally essenial (if body cannot make enough: arginine, cysteine, glutamine, glycine, proline, tyrosine, ex: if we don"t have enough phenylalanine (not consuming enough or have pku) have to supplement diet with tyrosine which becomes condiionally essenial. High-quality proteins contain all essenial amino acids: hisidine, leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine. Measuring protein quality: protein digesibility-corrected aa score (pdcaas): relected indirectly in %daily value for proteins on labels people adoping vegan/veg. diet mix & match. Egg white, ground beef, chicken, skim milk, tuna. Secondary structure: energeic preference" for beta-sheet (bulky side chains) or alpha-helix (smaller side chains) Quaternary structure: interacions between 2 or more proteins. Loss of stability due to heat, acid, or other harmful condiions.